Another take on the SingletonModel buiz..

 * Added Toolkit::classHeritage, returns an array of a classes ancestry
 * Added Toolkit::isSubClass(), returns a boolean comparison between two classes
 * Refactored SingletonModel tests into it's own testcase
 * Added tests for new Toolkit methods
 * Refactored Controller::getModel and Controller::getGlobalModel to use Toolkit::isSubClass() to determine model implementation
 * made SingletonModel::__clone() protected, too.. (should probably throw an exception too, eh?)
Only call a model's initialize method, if it has one.